I'm with FP, 30 Years War hands down. If you lived in a smaller German farming village you were unlikely to have any direct experience with the Allied militaries until 1945. Allied soldiers -even Soviet soldiers despite their poor reputation- were supplied through a reasonably effective logistics corps which is a far cry from the "find the nearest farm and steal their pigs" school of logistics practiced during the 30 Year War. Plus, the 30 Years War did last Thirty Years. Even if people weren't as effective and murdering and pillaging in 1640 they had a lot more time to do it.
If you lived in a smaller German farming village you were not a representative part of the German population in 1945.
The overwhelming majority of the demographic effect of the era of the Thirty Years' War in Germany is related to a couple of things that are only tangentially associated with military operations. First is the role of disease, which was
often (but not always) spread by troops and, when not by troops, by refugees from fighting. Disease, as it did in virtually every premodern war, was the big killer, killing 3 soldiers for every 1 who died fighting or of wounds. The second thing, malnourishment, exacerbated disease. It was primarily caused by relatively poor harvests from 1619 to 1628 and made significantly worse by the Habsburg hyperinflation in the early 1620s, which eroded purchasing power and made it much more difficult for urbanites to acquire food. Military contributions and raiding were both relevant, but minor compared to the economic crisis of the 1620s.
Obviously, both of these things were made worse by the war, but it's not clear
how worse. Modern authors have pointed out that mortality rates in early modern Europe were high
anyway. Furthermore, the aforementioned migration and severe holes in early modern record-keeping make it extremely likely that many of the individuals who disappear from territorial registers simply moved somewhere else and stayed there. In Germany, population declines were usually localized and irregular (things like the total depopulation of Magdeburg were extremely uncommon), and most attempts to aggregate them without accounting for holes in the data have severely overestimated death rates (and compounded that by neglecting to compare them to peacetime mortality rates).
Many sources agree that, in general (again, demographic estimates already had high error before the methodological issue of migration was raised), Germany's population did not reach the level of 1618 until about 1710-20. It is not clear that this can be primarily associated with the Thirty Years' War, because rather than an era of peace in central Europe - as with the century
before the war - there was an era of war. One suspects that things like the devastation of the Rhineland by Louis XIV's armies explain a great deal of the slow recovery. By comparison, after the Second World War, West Germany enjoyed an extended period of peace, security, immigration, and investment.
Sussing out whether the TYW or WWII was more "devastating" to Germany's population and economy is, at any rate, a very complicated endeavor, and like many other areas of history, what we actually know about the human and material costs, and what we can safely attribute to the war itself, are both more circumscribed than we might think.
Mouthwash - yes, they are, or at least 1000 replies. JohannaK, you actually made the 1000th, so the theoretical right to start a new one is with you.
Aw. I thought that there were no technical grounds forcing thread consolidation anymore.